Polymers are a mainstay of modern society, for example, widely used in fabricating textiles, upholstery, construction materials, various air, land or sea vehicles, and microelectronic devices and appliances. The inherent flammability of many polymers poses a significant threat, especially in enclosed or isolated spaces. Therefore, as synthetic polymers are used extensively in society as plastics, rubbers, and textiles, polymer flammability has been recognized as a safety hazard and remains an important challenge in polymer research.
Epoxy resins are prominent among thermoset polymers, employed as high performance adhesives, surface coatings, encapsulation matrices, and composites in applications ranging from aerospace transportation to microelectronics packaging. (Odian G. 2004 Principles of Polymerization, Fourth ed. Hoboken, N.J.: John Wiley & Sons, Inc.; Hergenrother, et al. 2005 Polymer 46(14):5012-5024; Rakotomalala, et al. 2010 Materials 3(8):4300-4327.) Epoxy resins, like many synthetic polymer materials, require low flammability for their safe use. While halogenated flame retardants (FR) are common additives that impart low flammability to materials, there is a growing concern over the potential health and environmental consequences of such additives. Halogenated flame retardants are known to release undesirable hydrogen halide gas upon combustion.
With respect to epoxy resins, efforts towards non-halogenated materials center on the integration of phosphorus, boron, or silicon into the cross-linked matrix. (Hergenrother, et al. 2005 Polymer 46(14):5012-5024; Rakotomalala, et al. 2010 Materials 3(8):4300-4327; Lu, et al. 2002 Prog Polym Sci 27(8):1661-1712; Levchik, et al. 2005 Polym Degrad Stabil 88(1):57-62; Lv, et al. 2013 Ind Eng Chem Res 52(27):9397-9404; Mauerer 2005 Polym Degrad Stabil 88(1):70-73; Toldy, et al. 2008 Polym Degrad Stabil 93(11):2007-2013; Weil, et al. 2004 J Fire Sci 22(1):25-40; Martin, et al. 2006 J Polym Sci Pol Chem 44(5):1701-1710; Martin, et al. 2006 J Polym Sci Pol Chem 44(21):6332-6344; Deng, et al. 2012 Ind Eng Chem Res 51(24):8178-8184; Devaraju, et al. 2013 Polym Composite 34(6):904-91 1; Gao, et al. 2013 J Appl Polym Sci 127(3):1842-1847.) However, non-halogenated flame retardant additives, such as alumina trihydrate, compromise the physical and mechanical properties of polymers when loaded at high levels.
Thus, there remains an urgent, on-going need for novel synthetic strategies toward a broad range of structurally and functionally diverse flame-retardant polymers.